The subject matter of this disclosure is generally related to optical analysis systems for analyzing a substance of interest, for example, crude petroleum, gas, water, or other wellbore fluids. For instance, the disclosed optical analysis systems use an integrated computational element (ICE) that has a frequency selective surface.
Information about a substance can be derived through the interaction of light from the ultraviolet (UV) to infrared (IR) ranges with that substance. The interaction changes characteristics of the light, specifically the frequency (color), intensity, polarization, and/or direction (e.g., through scattering, absorption or refraction). Chemical or physical properties of the substance can be determined based on the changes in the characteristics of the light interacting with the substance. For example, in certain applications, one or more properties of crude petroleum, gas, water, or other wellbore fluids can be derived in-situ in petroleum fields, more commonly referred to as oil fields, as a result of the interaction between these substances and light. For example, downhole instruments can use the interaction between light and substances found downhole for making fluid (oil, gas and water) and geological chemical and physical measurements at well sites.
Integrated computational elements (ICEs) are filters that transform light into chemical or physical information through the use of regression techniques. ICE filters (or simply ICEs) represent pattern recognition systems which recognize certain spectral patterns using vector regression techniques. Typically, an ICE is a substrate with multiple stacked dielectric layers (e.g., about 30 to 50 layers), each having a different refractive index from its adjacent layers. The ICE is configured to selectively pass predetermined fractions of light of different wavelengths. For instance, the number of layers N, the materials and the spacings of the N layers that compose the ICE are selected, e.g., using conventional methods for designing so called optical interference filters, so each wavelength of the light transmitted through the ICE can be weighted in a predetermined manner.
Because ICEs are configured to extract information from light modified by a sample without having to perform spectral analysis outside of the ICEs, they can be incorporated in low cost and rugged instruments. Hence, such ICE-based downhole instruments can provide a relatively low cost, rugged and accurate system for monitoring petroleum quality.
Like reference symbols in the various drawings indicate like elements.